In many countries wheeled road vehicles, such as cars, trucks, vans, buses, need to be tested usually yearly, before a road license is granted to the owner by the controlling authority. The required tests include factors such as wheel alignment, steering, and brake functioning, besides visual examination of components such as tires.
In recent years the European Economic Community has started to demand brake testing in a manner said to parallel brake operation under road conditions. Applicable standards include 96/96/UE, 92/55/EEC, 77/143/EEC, and 71/320/EEC. Most test stands in use today do not comply with these European standards Furthermore, as ABS systems have come into wider use, a need has arisen to test such braking systems under realistic conditions.
Also those wishing to purchase a used vehicle may order testing in order to verify beforehand whether the vehicle has faults which are either to be repaired by the seller or to be considered in determining an agreed purchase price. A vehicle buyer is however interested in matters which are of little concern to a licensing authority—for example, engine performance under load, state of the suspension, the state of the transmission, including the gearbox and factors such as gear slip in automatic transmissions. Prior art test stands may meet the requirements of the licensing authority but still do not provide all the information which is of interest to a buyer. A further significant limitation of existing test stands is that the twin rollers which support the front or rear wheels are made long enough to cover the vehicle width. This makes fault detection of an individual wheel difficult, and does not allow the testing of ABS braking systems. Furthermore, prior art test stands have no arrangement for verifying the accuracy of the test apparatus.
A further limitation of present-day test stands is an inability to test the vehicle automatic transmission, without dismantling same, and without driving the vehicle out of the testing station.
The state of the art can be gauged by review of recent US Patents.
In U.S. Pat. No. 6,192,303 Takakura et al. disclose a vehicle diagnosis apparatus. A portable diagnosing unit is connected to a vehicle-mounted electronic control unit. A stationary host computer receives data by wireless from several vehicles so equipped. Each vehicle is identified by a number, and a ROM contains a suitable computer program to carry out the diagnosis.
Yamaguchi et al. relate to the relationship between vehicle slip angle and the road surface in the device described in U.S. Pat. No. 6,308,115.
Lohberg et al propose a method for measuring yaw rates and other quantities described in U.S. Pat. No. 6,317,674. Two independent measuring channels are proposed. A control signal intended to effect a correction is produced by a logic controller.
There is therefor a need for a vehicle test apparatus which has the capacity to accurately measure a wider range of vehicle properties than are available in prior art test stands.
It is therefore one of the objects of the present invention to obviate the limitations of prior art vehicle test stands and to provide an apparatus which meets present day requirements, including information desired by a prospective vehicle buyer, such as suspension and wheel geometry, brake performance, and characteristics of engine performance and the condition of an automatic transmission.
It is a further object of the present invention to test and calibrate the dynamometer used for vehicle testing at high speed and under conditions similar to road conditions.
The present invention achieves the above objects by providing an apparatus for testing the brakes, wheel alignment, suspension, transmission, and engine of motorized wheeled vehicles, including means for calibrating said apparatus, comprising:
a platform arranged to allow a heavy vehicle to be placed thereon;
at least two pairs of high-inertia rollers supported by the platform and positioned to support either the front wheels or the back wheels of the vehicle, the rollers being drivable by a stationary vehicle resting thereon, each pair of the high-inertia rollers supporting one wheel of the vehicle;and sensor means connected to the rollers and data processing, display and recording means connected to the sensors.
In a preferred embodiment of the present invention there is provided a testing apparatus wherein the high-inertia rollers are connectable to at least one electric motor allowing the rollers to drive the vehicle wheels resting thereon.
In a most preferred embodiment of the present invention there is provided a testing apparatus further provided with a floating roller positioned between the inertia rollers and above the center thereof and being connected to means urging the floating roller upwards into contact with a vehicle wheel thereabove.
Yet further embodiments of the invention will be described hereinafter.
Due to the wide range of tests which can be performed by the apparatus described in the present specification, it is feasible that the apparatus would also be of interest to companies developing motor vehicles. Such companies may carry out hundreds of tests simultaneously, as described in MACHINE DESIGN, Mar. 7, 2002, p 114 “Mobile test system ready to roll—and grow” but would also be helped by an apparatus much easier to use for preliminary screening of new designs.
It will thus be realized that the novel device of the present invention also serves to reveal the interaction between the tested parameters. For example, in the course of executing a series of brake tests to determine brake fading and further characteristics, the reaction of the suspension is monitored, and faults such as bad shock absorbers or suspension distortion will be revealed and recorded.
The utility of the present invention is further enhanced by the possibility of adding further optional equipment such as flywheels (for testing large vehicles) and a power absorption unit (for applying a steady-state load for extensive engine, retarder and gearbox testing).
Most prior-art vehicle test stands are equipped with encoders providing 100 pulses per revolution. By using a 1000 pulse encoder, preferably 1200, accuracy is much improved, the finer resolution being needed particularly for calculation of accelerations and decelerations, and for testing gear slip in automatic gearboxes.
The invention will now be described further with reference to the accompanying drawings, which represent by example preferred embodiments of the invention. Structural details are shown only as far as necessary for a fundamental understanding thereof. The described examples, together with the drawings, will make apparent to those skilled in the art how further forms of the invention may be realized.